Abstract:Carbon nanotubes have been extensively investigated for developing polymer matrix nanocomposites and a number of such nanocomposites are already being used in various applications [1, 2]. Metallic composites, particularly those of aluminum, containing carbon nanotubes would offer distinct advantages over polymeric composites, but the development of metal matrix composites remains in its infancy [3] in spite of its great potential, primarily because of high fabrication costs and difficulty in scaling up. We have developed a scaleable chemical vapor infiltration technique [4, 5] which can be combined with electrophoretic deposition to form metal matrix nanocomposites with enhanced yield strength and varying levels of carbon nanotube loading. Specifically, catalytic chemical vapor deposition was used to infiltrate metal matrices with single and multiwall carbon nanotubes using carbon monoxide and acetylene as carbon sources. Vickers hardness numbers and stress-strain curves were measured to characterize the mechanical properties of the composites formed. It was found that the yield strength of iron-carbon nanotube composites increased up to 45% with about 1 wt % of infiltrated single wall carbon nanotubes, and 36% with ~1 wt % multiwall carbon nanotubes, relative to that of similarly treated pure iron matrices of the same piece density. Vickers hardness coefficients were also substantially enhanced - 74% and 96%, respectively, for composites with single and multiwall carbon nanotubes relative to the pure matrices. When acetylene is used as the carbon source, carbide formation can occur, which can be prevented by mixing acetylene with carbon monoxide. A reaction mechanism for carbide-free growth has been formulated and will be discussed. The same fabrication-infiltration technique in combination with electrophoretic deposition is being extended to steel and aluminum matrices. Results from these studies will be presented and compared with the data on iron-carbon nanotube composites. [1] A. Morgan, Material Matters 2, 20 (2007). [2] Z. Iqbal and A. Goyal, Carbon nanotubes/nanofibers and carbon fibers in Functional Fillers for Plastics (ed. Xanthos, M.) Ch 10 (WILEY-VCH Verlag GmbH & Co., Berlin 2005). [3] P.K. Rohatgi and B. Schultz, Material Matters 2, 16 (2007). [4] A. Goyal, D. A. Wiegand, F. J. Owens and Z. Iqbal, Journal of Materials Research 21, 522 (2006). [5] A. Goyal, D. A. Wiegand, F. J. Owens and Z. Iqbal, Chemical Physics Letters, 442, 365 (2007).